GIMP tips and tricks please

Is there any good GIMP tutorials? I am really interested in....
1. How do I unpack a zip file?
2. With some gray scales, it does not allow me to color it while keeping the shading, it just covers it in a flat layer. Help please
3. Downloading brushes? And where is the best place to get them

Any other tips and tricks, thanks.

1. You need to have Winrar or 7zip installed on your PC. After installing one, right-click on archive, then on "extract" and choose location.
2. Did you add a new layer? If so, did you change its mode from "Normal" to another one?
You can also change brushes mode but if you do it, you need to color on layer with grayscale.
3. I searched for new brushes mostly on deviantart. Using v.2.8 and above (not sureit  it works with 2.6, it's been ages since I used that one) you can also install Photoshop brushes.

2. Set the color layer mode to hard light, then it should be fine as long as the layer is above the greyscale.